One method and apparatus by which the presence and concentration of radon and its alpha-emitting daughters can be effectively detected and monitored is disclosed in U.S. Pat. No. 3,665,194 -- Alter et al., incorporated by reference. A sheet of solid state track-registration material (the alpha particle detector) is disposed in a protective environment at a location to be checked for the emission of radon. If the track-registration material becomes irradiated by alpha particles, minute damage "tracks" are created therein, which tracks can be enlarged and made visible by contact with a reagent to which the tracks display preferential checmical reactivity.
Apparatus is described in U.S. Patent Application Ser. No. 715,224 -- Ward filed (now U.S. Pat. No. 4,064,436) Aug. 18, 1976 (assigned to the assignee of the instant invention at the time of the filing thereof) for the reduction or removal of background noise caused by thoron gas (.sup.220 Rn) in uranium exploration which exploration is being conducted by the detection of radon gas (.sup.222 Rn) emanating from the ground. The objective is achieved by disposing in the path of the gases passing to the alpha particle detector a permselective membrane, which permits, but selectively retards, the passage therethrough of thoron and radon. The Ward patent is incorporated by reference.
Ordinarily this uranium exploration is carried out by burying in the earth inverted cup-shaped housings containing the track-registration material. The housings are set forth in a predetermined arrangement (e.g., a grid system) and permitted to remain for a preselected period of time (e.g., four weeks). Thereafter the housings and detectors are removed, the detectors are subjected to a chemical etching solution and the number of tracks etched on each detector is counted by micro-scopic inspection. Correlation of the results from the various housings are made in order to determine whether subsurface uranium ore is present and where.
Another method of uranium exploration substitutes an electronic solid state detector of alpha particles for the track registration material of the method described hereinabove. These electronic detectors may be used repetitively either in the same or new locations.